Low Danger

January 26, 2017

Low

Posted:
Jan 26, 2017 @ 6:35 am

The current avalanche danger is LOW for the west central Montana backcountry. Human triggered avalanches are still possible in isolated terrain.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for January 26, 2017. This danger rating does not apply to operating ski areas, expires at midnight tonight and is the sole responsibility of the U.S. Forest Service.

Weather and Snowpack

Mountain temperatures range from 12 F to 21 F in the region. Winds are 5 mph with gusts of 7 mph out of the WSW in the Bitterroot. Point Six, in the northern part of the advisory area, winds are reading 7 mph with gusts of 10 mph out of the WNW. Some snotels are not reporting this morning. The North Fork of the Jocko received 8 inches of snow in the last 24 hours with a SWE of .5 inches of water. The other sites that are reporting received 2-3 new inches of snow with .1 inches of water.

Logan and I did an extended tour in the Rattlesnake, yesterday. Tim and Greg took the sleds to Spruce Creek in the central Bitterroot. We dug several pits on multiple aspects and elevations. The instabilities in our snowpack are healing. We were not able to get any propagation in any of our pit tests. The new snow is very low density and has come in with the very little wind.

The primary avalanche concern is loose dry avalanches. These sluffs are small and very low energy. They will only be a concern if they carry you into a terrain trap.

The second avalanche problem is wind slabs. These are small and shallow located in isolated pockets on leeward terrain. You can identify these slabs by smooth rounded pillows on the surface near ridgelines.

The final avalanche concern is persistent slabs. There are three layers to examine in pits before committing to a slope. The interface of the new snow and old snow surface. The rain crust 40 cm to 50 cm from the surface. Finally, the basal facets near the ground. These layers have not propagated in any of our observers’ tests for nearly two weeks. We did get a public observation of propagation on the rain crust in an ECT on Mt. Fuji near, Lolo Pass. If you get propagation in your pit, choose to back off the slope and ride lower angle terrain.

Avalanche and Weather Outlook

Light snow this morning then clearing skies. High pressure will build, but there is a chance for some light accumulation of snow on Friday. With these conditions, the avalanche danger will remain the same.

Join us tonight at the University of Montana in the North Urey Lecture Hall at 6:00 pm for a free lecture on Introduction to Avalanches part 2.

If you are out in the backcountry, please send us your observations, these are very helpful in producing the advisory. Logan will issue the next advisory on January 28, 2017.

Ski and ride safe.

READ FULL ADVISORY

Problem 1 - Loose Dry

TYPE

Loose Dry
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.
SIZE

< 1 (Small)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Unlikely/Possible
The likelihood of an avalanche resulting from this problem.

Loose dry avalanches are the main concern. These are small and are very low energy. Not a concern unless they carry you into a terrain trap(cliff, rocks or trees).

Problem 2 - Wind Slabs

TYPE

Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
SIZE

1 (Small)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Unlikely/Possible
The likelihood of an avalanche resulting from this problem.

Small wind slabs located on isolated pockets on ridges.

Problem 3 - Persistent Slabs

TYPE

Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Persistent, Deep-Slab.
SIZE

1-2 (Small-Large)
The potential size of avalanche resulting from this problem.
LIKELIHOOD

Unlikely
The likelihood of an avalanche resulting from this problem.
IMAGE

There are 3 layers in the snowpack to pay attention to.

1) The crust that the new snow is on.

2) The rain crust that is 40cm to 50 cm from the surface

3) The basal facets on the ground.

Dig a pit to assess these layers before committing to any steep slope.

VIDEO

01/25/2017 Rattlesnake

GALLERY

Spruce Creek-25-Jan

Evaro Bowl1_25_17

Slope

Rattlesnake South Slope

Logan in a Pit

Slope

Evaro

PIt NE

Avalanche Class

Rattlesnake 01/25/2017

FORECAST & OUTLOOK

Danger Trend

Same Danger
Area Forecast

Light Snow

Light snow this morning then clearing skies. High pressure will build, but there is a chance for some light accumulation of snow on Friday. With these conditions the avalanche danger should remain the same.

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.